Problem: Solve for $x$ and $y$ using substitution. ${3x+2y = -3}$ ${y = -2x-5}$
Since $y$ has already been solved for, substitute $-2x-5$ for $y$ in the first equation. ${3x + 2}{(-2x-5)}{= -3}$ Simplify and solve for $x$ $3x-4x - 10 = -3$ $-x-10 = -3$ $-x-10{+10} = -3{+10}$ $-x = 7$ $\dfrac{-x}{{-1}} = \dfrac{7}{{-1}}$ ${x = -7}$ Now that you know ${x = -7}$ , plug it back into $\thinspace {y = -2x-5}\thinspace$ to find $y$ ${y = -2}{(-7)}{ - 5}$ $y = 14 - 5$ $y = 9$ You can also plug ${x = -7}$ into $\thinspace {3x+2y = -3}\thinspace$ and get the same answer for $y$ : ${3}{(-7)}{ + 2y = -3}$ ${y = 9}$